Conventional back-lit displays, such as those used in automotive audio, mobile multi media (MMM), and heating/ventilation/air-conditioning (HVAC) control heads, have been lit by a plethora of individual light sources such as miniature incandescent lamps or light emitting diodes (LEDs). Typically, for conventional design arrangements including a plurality of back-lit buttons, an individual LED is positioned behind an individual button to direct light towards a viewer. When individual light sources are used behind each button, the button typically includes a layer of diffusion to make a large button graphic appear even. To compensate for diffusion losses, a large amount light is directed at the back of the button. Not only is this design arrangement highly inefficient with respect to lighting utilization and the one-for-one arrangement of LED (or lamp)-to-button, but it also leads to several problems.
In a first example implementing incandescent lamps for light sources, between 80% and 90% of the electrical energy is undesirably converted to heat. To diminish the heat generation, costly solutions may include the relocation of components or the addition of heat sinking. In another example implementing LEDs for light sources, the light directed toward the viewer may undesirably vary. More specifically, undesirable color and intensity variation may occur from LED component to LED component. Because the viewer can distinguish the intensity and color variation within a batch of LEDs, these inherently undesirable characteristics of individual LEDs lead to color and intensity matching issues that have to be minimized prior to assembly of the back-lit display. Additional effort in minimizing these variables may call for matching sorted LEDs with specific resistors.
LED lighting for back-lit displays is also limited in color availability. Most LEDs are narrow spectrum light sources that, when observed by a viewer, are seen as highly saturated colors. If a desaturated or pastel color is desired, the color is typically produced by implementing a white LED with a filter placed directly over the LED or directly below the button. Although adequate for most applications, white LEDs are expensive, tend to have varying colors, and are inefficient to filter to certain colors. Alternatively, a desaturated or pastel color may also be produced by implementing a filtered incandescent lamp.
Thus, there is a need for an alternative device that may overcome the fallbacks of incandescent lamps or LEDs that illuminate back-lit displays.